To be honest,i don't follow the guidlines on the back as its never been correct for my two. I would personally make 3oz,see how much your LO drinks and that will give you a rough guide. If drinking it all then you know you can make 4oz the next time. I only drinking less than 2oz you could make just the 2oz with the next bottle iykwim?
Each baby is different,weigh different,and will drink different amounts. Your baby will tell you how much they want.